Allow building without terminal library

This reverts commit 0d3416e0c2.
cf. https://github.com/tats/w3m/pull/221
Bug-Chromium: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=46629

acinclude.m4

@@ -427,9 +427,7 @@ AC_ARG_WITH(termlib,
  AC_MSG_RESULT($with_termlib)
  test x"$with_termlib" = xyes && with_termlib="terminfo mytinfo termlib termcap tinfo ncurses curses"
  for lib in $with_termlib; do
-   AC_CHECK_LIB($lib, tgetent,
-                [W3M_LIBS="$W3M_LIBS -l$lib"; break],
-                [test "$lib" = curses && AC_MSG_ERROR([No terminal library found])])
+   AC_CHECK_LIB($lib, tgetent, [W3M_LIBS="$W3M_LIBS -l$lib"; break])
  done
 ])
 #

configure

@@ -8803,8 +8803,6 @@ eval ac_res=\$$as_ac_Lib
 $as_echo "$ac_res" >&6; }
 if eval test \"x\$"$as_ac_Lib"\" = x"yes"; then :
   W3M_LIBS="$W3M_LIBS -l$lib"; break
-else
-  test "$lib" = curses && as_fn_error $? "No terminal library found" "$LINENO" 5
 fi
 
  done